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Understanding the Nervous System

Feb 26, 2025

Lecture Notes on the Nervous System

Overview

  • Nervous system is the master control and communication system of the body.
  • Cells communicate via electrical signals (action potentials) and chemical signals (neurotransmitters).
  • Controls homeostasis, movement, sleep/wake cycles, hunger, endocrine system.

Main Functions of the Nervous System

  1. Sensory Input

    • Gathers information from internal and external environments.
    • Necessary for deciding actions.
  2. Integration

    • Analyzes and interprets sensory input.
    • Determines if a response is needed.
  3. Motor Output

    • Executes response to stimuli.
    • Example: A soccer player sees a ball and decides to kick it.

Divisions of the Nervous System

Structural Divisions

  • Central Nervous System (CNS)

    • Composed of the brain and spinal cord.
  • Peripheral Nervous System (PNS)

    • Composed of nerves that connect the body to the CNS.

Functional Divisions

  • Central Nervous System

    • Site of integration for sensory information and motor response planning.
  • Peripheral Nervous System

    • Conducts sensory (afferent) and motor (efferent) functions.

Peripheral Nervous System Subdivisions

  • Sensory (Afferent) Division

    • Carries sensory stimuli to the CNS.
    • Subdivided into:
      • Somatic Sensory Division: From muscles, bones, skin.
      • Visceral Sensory Division: From organs (abdominal, pelvic, thoracic cavities).
  • Motor (Efferent) Division

    • Carries motor responses from CNS to effectors.
    • Subdivided into:
      • Somatic Motor Division: Controls skeletal muscles (voluntary).
      • Autonomic Nervous System: Controls smooth muscles, cardiac muscles, glands (involuntary).
        • Further divided into the parasympathetic and sympathetic divisions.

Histology of Nervous Tissue

  • Consists of many cells with little extracellular space.
  • Two main cell types:
    • Neurons: Structural and functional units.
    • Neuroglia: Supportive cells.
      • Types in CNS: Astrocytes, Microglial cells, Ependymal cells, Oligodendrocytes.
      • Types in PNS: Schwann cells, Satellite cells.

Astrocytes

  • Most abundant and versatile neuroglia.
  • Functions:
    • Anchor neurons and blood vessels.
    • Regulate environment, clean up excess neurotransmitters and ions.
    • Form the blood-brain barrier.
    • Repair damaged tissue (forms scar tissue).

Microglial Cells

  • Act as phagocytes to clean up debris and pathogens.

Ependymal Cells

  • Ciliated cells that circulate cerebrospinal fluid (CSF).

Oligodendrocytes

  • Form myelin sheath in CNS to speed up signal transmission.

Schwann Cells

  • Form myelin sheath in PNS.

Satellite Cells

  • Surround cell bodies in PNS, functionally similar to astrocytes.

Structure of Neurons

  • Cell Body: Metabolically active, contains nucleus, endoplasmic reticulum, etc.
  • Dendrites: Short, branched processes that receive input.
  • Axon: Long process that conducts action potentials.
    • Arises from the axon hillock.
    • Ends in axon terminals containing neurotransmitters.

Terminology

  • Axolemma: Plasma membrane of the axon.
  • Axoplasm: Cytoplasm within the axon.

Conclusion

  • Neurons and neuroglia play essential roles in the functioning of the nervous system.
  • Understanding the structure and function is crucial for learning how the nervous system influences all aspects of physiology.